In the wake of the March 15 New Zealand shootings, advocates for new gun restrictions in New Zealand have pointed to Australia as "proof" that if national governments adopt gun restrictions like those of Australia's National Firearms Agreement, then homicides will go into steep decline.
Source: Australia's Gun Laws and Homicide: Correlation Isn't Causation | Mises Wire
The problem is that the numbers don't back this up. People like to point out that homicides dropped after gun control measures were instituted there, however the homicide rate was already in decline long before such measures were instituted. This is generally true in most of the Western world. Emotional knee-jerk reactions are most likely not going to prevent mass shootings.